Apparatus For Sensing User Input

ABSTRACT

An apparatus utilizes multiple strain gauge (“SG”) sensing units which are each disposed adjacent an inner surface of the device housing. Electrical voltage generated by the SGs is amplified by one or more amplifiers to maximize the resolution between a voltage output of an SG when in a non-pressed state and a voltage output of the SG when in a pressed state. Additionally, an electronic circuit is configured to identify a baseline voltage output for an SG over a period of time for comparing to a voltage output for the SG when the SG is in a pressed state such that the pressed state of the SG can be identified by the electronic circuit by comparing a current output voltage of the SG to the identified baseline voltage.

BACKGROUND

Electronic devices sometimes include buttons that protrude from an outeror exterior surface of a housing of the electronic device. In general,the buttons serve as physical inputs to allow users to cause changes todevice functions (such as volume control, displayactivation/deactivation, switching to/from vibrate mode, etc.). Suchbuttons are typically positioned on the sides of electronic devices suchas smartphones, other mobile cellular devices, tablet computers,notebook computers, and desktop computers.

SUMMARY

An apparatus for sensing user input to an electronic device isdescribed. The apparatus utilizes multiple strain gauge (“SG”) sensingunits which are each disposed adjacent an inner surface of the devicehousing. The SG sensing units are configured to detect a particular typeof user input to the device based on at least one of: the magnitude ofstrain applied to the SG sensing units, the relative location of theapplied strain, and the duration of the applied strain. The SG sensingunits can be arranged in particular configurations to sense appliedstrain along, for example, a lengthwise dimension of the device and/or awidthwise dimension of the device. Electrical voltage generated by theSGs is amplified by one or more amplifiers to maximize the resolutionbetween a voltage output of an SG when in a non-pressed state and avoltage output of the SG when in a pressed state. Additionally, anelectronic circuit is configured to identify a baseline voltage outputfor an SG over a period of time for comparing to a voltage output forthe SG when the SG is in a pressed state such that the pressed state ofthe SG can be identified by the electronic circuit by comparing acurrent output voltage of the SG to the identified baseline voltage.Hence, the described sensing apparatus provides methods and techniquesfor receiving user input to an electronic device while also replacingphysical buttons that protrude above an exterior surface of the device.

In one innovative aspect of the specification, an apparatus for sensinguser input provided on an exterior surface of an electronic device isdescribed. The apparatus is configured for inclusion in an electronicdevice (such as a smart phone, tablet device, or personal computer) andcan be configured to sense user input provided on an exterior surface ofan electronic device. In general, in one aspect, the apparatus caninclude a first strain gauge configured to couple with a housing of anelectronic device; an amplifier electrically coupled to the first straingauge and configured to amplify an electrical property of the firststrain gauge; an analog-to-digital converter electrically coupled to theamplifier; and an electronic circuit electrically coupled to the firststrain gauge. The electronic circuit can be configured to (i) receive afirst parameter signal from the analog-to-digital converter in responseto user input that interacts with the housing over a location of thefirst strain gauge, (ii) determine a value for the first parametersignal, (iii) compare the determined value of the first parameter signalto a maximum value associated with the analog-to-digital converter, and(iv) adjust an amplification level of the amplifier in response tocomparing the determined value of the first parameter signal to themaximum value associated with the analog-to-digital converter.

These and other embodiments can each optionally include one or more ofthe following features. Adjusting the amplification level of theamplifier in response to comparing the determined value of the firstparameter signal to the maximum value associated with theanalog-to-digital converter can include adjusting the amplificationlevel to a highest available amplification multiplier that does notcause an output of the amplifier to exceed a maximum input value for theanalog-to-digital converter over a period of time. Adjusting theamplification level of the amplifier in response to comparing thedetermined value of the first parameter signal to the maximum valueassociated with the analog-to-digital converter can include determining,by the electronic circuit, that the first strain gauge has experiencedphysical damage; and in response to determining that the first straingauge has experienced physical damage, reducing the amplification levelof the amplifier to adjust for an increased voltage output of the firststrain gauge due to the damage to the first strain gauge. Determiningthat the first strain gauge has experienced physical damage can includeidentifying that a baseline output value of the analog-to-digitalconverter has increased above a threshold amount for a specified periodof time.

Adjusting the amplification level of the amplifier in response tocomparing the determined value of the first parameter signal to themaximum value associated with the analog-to-digital converter caninclude reducing the amplification level of the amplifier such that anoutput voltage of the amplifier does not exceed a maximum input voltagefor the analog-to-digital converter when pressure is applied to thefirst strain gauge by a user. The electronic circuit can be configuredto adjust the amplification level of the amplifier in response todetermining that an output voltage of the amplifier has exceeded amaximum input voltage associated with the analog-to-digital converter.The electronic circuit can be configured to adjust the amplificationlevel of the amplifier in response to determining that an output voltageof the amplifier is outside of an acceptable input voltage rangeassociated with the analog-to-digital converter. The electronic circuitcan be further configured to (v) determine a baseline output value forthe analog-to-digital converter over a period of time; (vi) compare thedetermined value for the first parameter signal to the baseline outputvalue; and (vii) indicate that a first type of user input has beenreceived in response to comparing the determined value for the firstparameter signal to the baseline output value. The electronic circuitcan be further configured to (v) sample outputs of the analog-to-digitalconverter at a first sampling rate; (vi) receive one or more signalsindicating that the electronic device is in an inactive mode; and (vii)reduce the sampling rate for sampling outputs of the analog-to-digitalconverter to a second sampling rate in response to receiving the one ormore signals indicating that the electronic device is in an inactivemode. The electronic circuit can be further configured to (v) sampleoutputs of the analog-to-digital converter at a first sampling rate;(vi) receive one or more signals indicating that the electronic devicehas entered an active mode; and (vii) increase the sampling rate forsampling outputs of the analog-to-digital converter to a second samplingrate in response to receiving the one or more signals indicating thatthe electronic device has entered the active mode.

The subject matter described in this specification can be implemented inparticular embodiments and can result in one or more of the followingadvantages. The apparatus of this specification allows devicemanufacturers to produce electronic devices that have a reduced quantityof buttons protruding from an exterior surface of the device housing.More particularly, reducing the number of buttons can minimize stepsrequired during execution of manufacturing and/or machining operationswhen producing device housings in substantial volumes. Furthermore, useof the SG sensing units described in this specification can reduce theamount of circuit components (wires, capacitors, etc.) as well as powerconsumption typically required to enable sensing functions provided bymechanical buttons. Additionally, electrical components can amplify ormodify electrical signals received from components of a strain gage toincrease detectability between a sensed voltage when a strain gage isbeing pressed as compared to a baseline sensed voltage. Furthermore,amplification of electrical signals received from components of an SGsensing unit can be adjusted to account for damage to a strain gage ordegradation over time of a strain gage. The apparatus of thisspecification further allows for a baseline sensed voltage to beidentified for comparison to sensed voltages indicative of a userapplying pressure to a strain gauge. Furthermore, various powermanagement techniques for reducing power consumption (such as, forexample, adjustment of sampling rates in response to detectedparameters) are described.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates diagrams associated with an apparatus for sensinguser input to an example electronic device.

FIG. 2 illustrates diagrams that include multiple strain gauges that canbe used in the apparatus of FIG. 1.

FIG. 3 illustrates diagrams that include resistor configurations, anexample bridge circuit, an amplifier, and analog-to-digital converterthat can be implemented to sense user input to an electronic device.

FIG. 4 illustrates a graph of changes to ambient temperature andbaseline output voltage of a strain gauge over time.

FIG. 5 illustrates a graph of changes to a sampling rate for a straingauge over time.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

An apparatus for sensing user input to an electronic device isdescribed. The apparatus utilizes multiple strain gauge (“SG”) sensingunits which are each disposed adjacent an inner surface of a housing ofthe electronic device. The apparatus includes an electronic circuit thatelectrically couples to each SG sensing unit. The electronic circuit isgenerally configured to receive parameter signals in response to userinput that interacts with the housing.

User input to the device can include strain applied to an area of theouter surface of the housing. The area can be either adjacent to, orsubstantially adjacent to, a particular SG sensing unit that is affixedto an inner surface of the housing on the other side of a housing wallthat defines the inner and outer surfaces. In response to strain appliedto the SG sensing unit, the SG sensing unit senses a particular type ofuser input to the device based on at least one of: a magnitude of theapplied strain, the relative location and of the applied strain, or aduration of the applied strain.

In general, each SG sensing unit includes multiple individual straingauges that each have a particular resistance attribute. The SGs can bearranged in a particular configuration to form a single SG sensing unitand each SG sensing unit can receive a voltage signal of a predefinedvoltage value. One or more output voltage signals received from each SGsensing unit are then measured by the electronic circuit and thenconverted into an example parameter signal. The output voltage signalsare measured to detect any shifts or changes to the correspondingvoltage value of the applied signal.

Applied strain to the outer surface of the housing can cause slightphysical changes (e.g., expansion or contraction) to at least one SG ofa SG sensing unit. The physical changes can cause a change in aresistance attribute of a SG. The change in the resistance attributecauses a corresponding change in the measured output voltage value and,thus, indicates a differential voltage signal that is received andmeasured by the electronic circuit. A range of differential outputvoltage signal values can be mapped to individual user input types. Themapped values can be used by the electronic device to detect ordetermine particular user input types based on a characteristic of theapplied strain and the corresponding signal value caused by the appliedstrain.

The electronic circuit can identify a baseline output voltage for the SGsuch that measured output voltage values can be compared to the baselineoutput voltage to determine if a change in the measured output voltagehas occurred. For example, the electronic circuit can identify a runningaverage for output voltage over a period of time (e.g., ten minutes) toestablish a baseline output voltage value. In some cases, sudden orbrief spikes in output voltage are ignored by the electronic circuitwhen identifying the baseline output voltage. The electronic circuit cancontinually compare current output voltage samples to the baseline todetermine if a change in the measured output voltage indicative of auser applying pressure to a SG has occurred.

Each SG sensing unit can additionally include an amplifier foramplifying the analog output voltage of the SG prior to the outputvoltage reaching an analog-to-digital converter (ADC). The amplifier canapply a multiplier to the analog output voltage to increasedetectability of changes to the output voltage due to pressure appliedto the SG by a user. The electronic circuit can adjust the amount ofamplification applied by the amplifier to prevent the output voltagefrom “railing” or exceeding a voltage range of detectable outputvoltages. For example, the electronic circuit can control the amplifierto amplify the output voltage such that a maximum value of the amplifiedoutput voltage that does not exceed +/−3 volts.

The electronic circuit can also implement power management processes toreduce power consumption of the SG sensing units. For example, theelectronic circuits can reduce the sampling rate for detecting changesin the output voltage of SGs in response to detected parameters. Forexample, the sampling rate can be reduced when a mobile device isplugged in and in a relatively horizontal position, as another example,the sampling rate can be reduced when the mobile device is attached to adocking station. As another example, the sampling rate can be reducedwhen a proximity detector of the mobile device determines that themobile device is near something, such as in a user's pocket.

FIG. 1 depicts diagrams associated with an apparatus 100 for sensinguser input to an example electronic device. Apparatus 100 generallyincludes a housing 102 that can later receive multiple electroniccomponents to form user device 104. In general, user device 104 caninclude smartphones, mobile devices, cellular devices, smarttelevisions, laptop computers, tablet computers, notebook computers,desktop computers, electronic readers, home automation devices, or avariety other types of computing devices or consumer electronic devices.

Apparatus 100 further includes coupling plate 106 and multiple SGsensing units 108 (hereinafter “sensing unit 108”). As discussed in moredetail below, each sensing unit 108 can include multiple strain gaugesthat can form sets of strain gauges that are arranged in a particularconfiguration within the unit. As generally shown, housing 102 caninclude a housing wall having an outer surface 110 corresponding to afirst side of the wall and an inner surface 112 corresponding to asecond side of the wall that is opposite the first side. Similarly,plate 106 can have a first side 114 and a second side 116 that isopposite the first side 114.

In some implementations, plate 106 can include multiple sensing units108 affixed to first side 114. As shown, plate 106 can be affixed orbonded to inner surface 112 by adhesive 118 that can be disposedgenerally intermediate second side 116 and housing wall 103. Plate 106can be formed from a variety of different materials such as steel,fiberglass, hardened plastic or other materials having properties thatenable plate 106 to be affixed to wall 103. Adhesive 118 can be anyadhesive material or compound such as glue, epoxy resin, bonding agent,or other materials suitable to securely affix/attach plate 106 to innersurface 112 of housing wall 103. Additionally, although identified as anadhesive, a variety of mechanical based fastening means suitable tosecurely affix/attach or couple plate 106 to inner surface 112 can alsobe utilized.

Housing 102 can receive multiple electronic components to form userdevice 104, which includes cover glass 120. Hence, apparatus 100 caninclude an example electronic circuit 122 that is disposed internallywithin device 104. Wire(s)/conductor(s) 124 can electrically couple, tocircuit 122, one or more strain gauge sets within sensing unit 108. Insome implementations, the electronic circuit 122 includes an amplifierfor amplifying the voltage of electronic signals received from the oneor more strain gauges. The electronic circuit 122 can additionallyinclude an analog-to-digital converter (ADC) for converting voltagesreceived from the one or more strain gauges to digitally quantizedvalues. In some implementations, the amplifier and/or ADC can beimplemented separately from the electronic circuit 122 and can bepositioned along the electrical communication path of thewires/conductors 124 between the electronic circuit and the one or morestrain gauges. In some implementations, the user device 104 includes aseparate amplifier and ADC for each strain gauge to individually amplifyand digitally quantize individual voltage signals from each straingauge.

As discussed in more detail below, an example user can provide aparticular type of user input to device 104 by applying a push force 118that can vary in push force magnitude and push force duration and/orfrequency. Push force 118 provides a corresponding strain force that isapplied to a particular SG set in respective sensing units 108 affixedto inner surface 112 of housing wall 103. In general, sensing units 108can be arranged in particular configurations to sense/detect appliedstrain along, for example, a lengthwise (L) dimension of device 104and/or a widthwise (W) dimension of device 104.

The applied strain can be detected by a parameter signal received by oneor more components of circuit 122. A value of the detected parametersignal can correspond to a particular type of user input. In someimplementations, the type of user input can be viewable via a displaydevice through cover glass 120. Different input types can include, forexample, user input to adjust an audio volume output of user device 104,user input to activate or deactivate a display device of user device104, user input to activate or deactivate a vibrate mode of user device104, and/or user input to adjust the volume of a ring tone of userdevice 104. In alternative implementations, a variety of different userinput types can be detected based, at least in part, on a particularvalue of the detected parameter signal.

As an example, apparatus 100 can be used in the followingimplementation. A user, Frank, wants to change the volume on a computingdevice, e.g., Frank's smartphone. Apparatus 100 can be implementedwithin Frank's smartphone such that sensing units 108 are disposedalong, for example, a lengthwise edge of Frank's smartphone. When Frankpresses a part of the smartphone housing associated with a volumesetting a particular strain gauge within sensing unit 108 is strained.

In response to the press applied by Frank, a change in a differentialvoltage value is detected by an electronic circuit disposed withinFrank's smartphone. The smartphone can be configured to detect thedifferential voltage value and associate particular values with, forexample, a volume press because the detected voltage change exceeds athreshold voltage change. A duration of the voltage change is measured,and the electronic circuit (which can be part of a microprocessor)outputs a value which indicates to the microprocessor that it is tochange the volume of an audio signal that is being output by a speakerof Frank's smartphone.

In some implementations, the electronic circuit 122 includes an ADC thatconverts the differential voltage value to a digital quantized value.For example, differential voltages ranging from −3V to 3V output by thesensing unit 108 can be converted to ADC units or “counts” ranging from0 to 10,000. This range of ADC counts can be divided into a number ofdiscrete ranges (e.g., five ranges of 2000 counts each or six ranges of1666 counts each). When the example user presses a part of thesmartphone housing associated with the volume setting strain gauge, anoutput voltage of the corresponding sensing unit 108 is converted to aquantized count number by the ADC. The output value of the ADC can becategorized into one of the discrete count ranges to identify aparticular input indicated by the user. For example, a volume of thesmartphone can be increased at varying rates based on the identifiedcount range for a particular output value of the ADC.

FIG. 2 illustrates diagrams that include multiple strain gauge unitsthat can be used in sensing units 108 of apparatus 100. As shown, theimplementation of FIG. 2 includes multiple technical features describedabove with reference to FIG. 1. In particular, FIG. 2 illustrates, inpart: 1) an isolation (ISO) view that generally depicts multipleindividual sensing units 108 attached to plate 106 that is affixed toinner surface 110 of housing wall 103; and 2) a cross-section (X-sec)view that depicts plate 106 attached/affixed to inner surface 110 ofhousing wall 103.

Each sensing unit 108 can include multiple strain gauge units 208 thatform sets of strain gauges that are arranged in a particularconfiguration within sensing unit 108. In some implementations, at leasttwo SGs 208 can form a SG set 208 a/b and multiple SG sets 208 a/b canform a SG grouping 210. When disposed against, or affixed to, innersurface 110, multiple SG sets 208 a/b can be arranged in particularorientations relative to each other. For example, a first SG set 208 acan be arranged in a first orientation corresponding to a firstdimension so as to detect or measure applied strain along the firstdimension. Likewise, a second SG set 208 b can be arranged in a secondorientation corresponding to a second dimension so as to detect ormeasure applied strain along the second dimension.

In general, the first orientation and the first dimension can bedifferent from the second orientation and the second dimension. In someimplementations, when user device 104 is positioned generallylongitudinally upright (e.g., when held by a user), the firstorientation can correspond to a vertical orientation and the firstdimension can correspond to a lengthwise (L) dimension. Further, when inthis longitudinally upright position, the second orientation cancorrespond to a horizontal orientation and the second dimension cancorrespond to a widthwise (W) dimension.

In the implementation of FIG. 2, when disposed within user device 104,SG grouping 210 can have a SG set 208 a that includes two SGs 208disposed in a horizontal orientation (when the device is upright) tomeasure applied strain to surface 112 in the widthwise dimension.Moreover, SG grouping 210 can also have a SG set 208 b that includes twoSG units 208 disposed in a vertical orientation (when the device isupright) to measure applied strain in the lengthwise dimension. Asshown, SGs 208 of SG grouping 210 can each be arranged in a parallelconfiguration, relative to each other, and can be disposed generallyalong the lengthwise dimension of a wall 103 (e.g., a sidewall) ofhousing 102.

When installed within user device 104, each SG grouping 210 of sensingunit 108 can be used to detect or sense user input in the form ofapplied force to surface 112. The applied force can cause SGs 208 tochange in electrical characteristics, to cause the electronic circuit122 to sense an increased strain. User device 104 can be configured torecognize the increased strain as corresponding to different user inputtypes such as a user pushing, swiping, tapping, squeezing or otherwisetouching a particular area on a sidewall wall of user device 104.

For example, when a user pushes on an edge or sidewall of housing 102that is adjacent a SG 208, the housing and plate 106 can bend or flex,causing SG 208 to change in electrical characteristics (e.g., theresistance of resistors change within a particular strain gauge), whichaffects the voltage of an electrical signal applied to the SG 208 andwhich causes the electronic circuit 122 (analyzing the electricalsignal) to sense an increased strain along, for example, the lengthwisedimension of device 104. Accordingly, user device 104 senses a push onthe edge of housing 102 and can indicate to the user, via an exampledisplay device (protected by cover glass 120), the particular input typeassociated with the user's push/touch. In some implementations, multiplesensing units 108 can be disposed or positioned along an edge orsidewall of housing 102 in order to sense or detect the particular inputtype and/or the proximate location of the push applied along the lengthof device 104. The electronic circuit 122 can analyze the electricalsignal that is received from each of the SG set 208 a and SG set 208 b.

As an overview of the terminology used herein, user device 104 mayinclude multiple sensors or sensing units 108. Each sensing unit 108 mayinclude two strain gauge sets indicated as features 208 a and 208 b. Asan example, strain gauge set 208 a can be oriented vertically and straingauge set 208 b can be oriented horizontally. Each strain gauge set 208a or 208 b includes two individual strain gauge units 208. Moreparticularly, and stated another way, each sensing unit 108 includesfour strain gauge units 208 or resistors 208 (discussed below withreference to FIG. 3) which form the two strain gauge sets 208 a/b orcircuit branches (discussed below with reference to FIG. 3). Referencefeature 210 refers to a strain gauge grouping that includes the fourindividual strain gauges 208 that collectively form a single sensor 108.

FIG. 3 illustrates diagrams that include resistor configurations, anexample bridge circuit 302, and various other electronic components thatcan be used to sense user input to an electronic device. As discussedabove, each sensing unit 108 includes multiple individual SGs 208 thateach have a particular resistance attribute. Hence, as shown in FIG. 3,in alternative implementations SG 208 can be depicted as one ofresistors (R1-R4) that each have an initial resistance value orresistance attribute which can, in some implementations, change inresponse to applied pressure. In particular, sensing unit 108 can bemodeled or depicted as bridge circuit 302 that includes positive(voltage polarity) output 308 and negative (voltage polarity) output310.

As shown, in some implementations, resistor orientation 304 can includeresistors R2 and R4 having a horizontal orientation so as to measureapplied strain in the widthwise (W) dimension, while resistors R1 & R3(vertical orientation) remain relatively fixed when strain is applieddue to their orientation and, thus, do not measure applied strain. Incontrast, resistor orientation 306 can include resistors R2 and R4having a vertical orientation so as to measure applied strain in thelengthwise (L) dimension while resistors R1 & R3 (horizontalorientation) remain relatively fixed when strain is applied due to theirorientation and, thus, do not measure applied strain.

In general, when a particular set of resistors are disposedperpendicular to a particular strain direction, that particular resistorset will generally not measure strain associated with that particularstrain direction. For example, as shown in resistor orientation 304, fora strain force applied in the widthwise (W) dimension/direction, SG set208 a is perpendicular to the strain direction and, thus, will generallynot measure applied strain. However, SG set 208 b is parallel to thestrain direction and will measure applied strain. Further, as shown inresistor orientation 306, for a strain force applied in the lengthwise(L) dimension/direction, SG set 208 b is perpendicular to the straindirection and, thus, will generally not measure applied strain. However,SG set 208 a is parallel to the strain direction and will measureapplied strain.

In general, bridge circuit 302 includes two branches. A first branch isindicated by R1 & R3 and the output node (for output 308) intermediateR1 & R3. A second branch is indicated by R2 & R4 and the output node(for output 310) intermediate R2 & R4. Bridge circuit 302 can receive anapplied voltage (VCC). Electronic circuit 122 can receive or detect adifferential voltage signal 312 in response to a change in theresistance attribute of any one of resistors R1-R4. In someimplementations, circuit 122 provides the VCC voltage signal and canthen execute a basic comparator circuit to analyze signal 312 relativeto the VCC signal. The analysis can enable circuit 122 to detect ordetermine the extent to which the measured value of signal 312 indicatesa deviation from the initially applied VCC voltage value. In someimplementations, the differential voltage signal 312 is passed throughan amplifier 314 and analog-to-digital converter (ADC) 316 prior toreaching the electronic circuit 122. In some implementations, theamplifier 314 and/or the ADC 316 are implemented as part of theelectronic circuit 122.

The ADC 316 can be, for example, a 24-bit ADC that quantizes inputvoltages into ADC units or “counts.” For example, the ADC can quantizeinput voltages into a range of values from 1 to 10,000 counts. The ADC316 can additionally have an allowable input voltage range. For example,the allowable input voltage range for the ADC 316 can be from −3 V to +3V.

During operation, and when disposed along inner surface 110 within userdevice 104, sensing unit 108 can detect applied strain in response to atouch force that is applied to a certain location of housing wall 103(e.g., an edge/sidewall of user device 104). For example, and as notedabove, user input in the form of applied strain to the edge of device104 can cause parameter signals to be received by electronic circuit122. The parameter signals can be received in response to user inputdetected by sensing unit 108, e.g., SG grouping 210, and can indicate auser input of a particular type, e.g., volume adjustment, activatevibrate mode, etc. Hence, detection of the user input can cause acorresponding response from device 104, e.g., indication on the displaydevice associated with a volume level increasing or decreasing.

For example, and with reference to bridge circuit 302, sensing unit 108can include SG set 208 a (resistors R1 & R3) that indicates a parametersignal having a first voltage value (via output node 308). Sensing unit108 can further include SG set 208 b (resistors R2 & R4) that indicatesa parameter signal having a second voltage value (via output node 310).The first voltage value and the second voltage value can be indicatedconcurrently in response to the user input of a particular type thatcauses a particular corresponding response from user device 104.

In some examples, applied strain in the W-dimension can cause physicalchanges to SG set 208 b that in turn causes the resistance attribute ofresistors R2 & R4, measured in ohms, to change (either increase ordecrease) by a predefined amount based on the magnitude of the appliedforce. Accordingly, presuming all resistance values in circuit 302 aregenerally the same, the change in a resistance attribute of R2 & R4 willcause a corresponding change in the voltage value measured at output310. Thus, a differential voltage signal 312, relative to outputs 308and 310, will be measured or detected by electronic circuit 122. In someimplementations, the differential voltage signal 312 can be, forexample, in the microvolt or the millivolt range. Thus, the differentialvoltage signal 312 can be amplified by the amplifier 314. As previouslydescribed, the amplifier 314 can be implemented as a standalone circuit,or as part of the electronic circuit 122.

In some implementations, the difference between the differential voltagesignal 312 when the sensing unit 108 is not being pressed and thedifferential voltage signal 312 when the sensing unit 108 is beingpressed can be, for example, 100 mv or smaller. The amplifier 314 canamplify the differential voltage signal 312 to increase the resolutionof the difference between the differential voltage signal 312 when thesensing unit 108 is being pressed and the differential voltage signal312 when the sensing unit 108 is not being pressed. In someimplementations, the amplifier 314 is adjustable and the amplificationlevel of the amplifier 314 is controlled by the electronic circuit 122.The electronic circuit 122 can control the amplifier 314 to amplify thedifferential voltage signal 312 such that the resolution of thedifference between the differential voltage signal 312 value indifferent states is maximized while avoiding “railing” (i.e., exceedinga maximum voltage) of the signal.

For example, the ADC 316 can have an allowable input voltage range suchthat input voltages outside of that range are not accurately convertedto a digitally quantized value. For example, the ADC 316 can have anallowable input range of −3V to +3V. If the output of the amplifier 314is greater than +3V or less than −3V, the ADC 316 is not able toaccurately convert the input signal to a number of ADC units or“counts.” The electronic circuit 122 therefore controls the voltagemultiplier of the amplifier 314 such that the output of the amplifier314 does not fall outside of the allowable voltage range for the ADC316. In some implementations, the allowable voltage range can be definedby a component other than the ADC 316. For example, the electroniccircuit 122 can define the allowable voltage range for output voltagesof the amplifier 314.

In some implementations, the range of values for the differentialvoltage signal 312 produced by the bridge circuit 302 can change overtime due to factors such as damage to the sensing unit 108, wear andtear, changes in temperature, changes in atmospheric pressure, ordegradation of components of the sensing unit 108 over time. Theelectronic circuit 122 can control the amplification level of theamplifier 314 as the range of values of the differential voltage signal312 changes such that the output of the amplifier 314 is maximized whilestill preventing the output of the amplifier 314 from being outside ofthe acceptable voltage range for the ADC 316.

For example, at an initial point in time (e.g., time of manufacture ortime of activation) the differential voltage signal 312 that serves asthe input to the amplifier 314 can range between 50 mV when the sensingunit 108 is in an unpressed state and 325 mV when the sensing unit 108is being pressed with a maximum amount of force within a normal forcerange for a user. The amplification of the amplifier 314 can be set to8× in this example to amplify the signal 8 times. This will increase theresolution of the signal while ensuring that the voltage does not exceeda maximum allowable voltage value of 3V. In this example, amplifying themaximum voltage range value of 325 mV by 8X gives a maximum output valueof the amplifier 314 of 2.6V, which is below the maximum allowablevoltage value of 3V. In some implementations, the amplification providedby the amplifier 314 can only be multipliers that are powers of 2. Inother implementations, other multiplier values for the amplificationprovided by amplifier 314 are possible. For example, continuing with theabove example, a 9λ amplification could be applied because the result ofamplifying the maximum differential voltage signal 312 of 325 mV valueby 9× is 2.925V, which is still less than the maximum allowable voltagevalue of 3V.

In some implementations, a manufacturing test can be performed todetermine an initial amplification level for the amplifier 314. Forexample, one or more robots can trigger one or more sensing units 108 ofa computing device as part of a manufacturing process. The robots canapply varying amounts of pressure to the sensing units 108 and theoutput of the ADC 316 can be measured at the various different pressurelevels. The amplification level of the amplifier 314 can be set duringthis testing process such that the output voltage of the amplifier 314does fall outside of the acceptable voltage range for the ADC 316 when ahigh level of pressure is applied to the sensing unit 108 by the one ormore robots. In some implementations, other parameters in addition tothe amount of pressure applied to the sensing units 108 are varied todetermine the correct amplification level for the amplifier 314. Forexample, temperature and ambient pressure in the environment of thecomputing device can be varied as part of the manufacturing test fordetermining an initial amplification level of the amplifier 314. In someimplementations, amplifiers for each of the sensing units 108 of thecomputing device are individually calibrated. In some implementations,computing devices for which the output of the ADC 316 exceeds athreshold value for a particular amplification level of the amplifier314 at a particular pressure (and/or temperature, ambient pressure) arediscarded.

Continuing with the above example, the range of values of thedifferential voltage signal 312 that serves as the input to theamplifier 314 can change over time. For example, a user might drop amobile device that includes the sensing unit 108 which can dent aportion of the sensing unit 108 and cause a baseline output voltage ofthe bridge circuit 302 to increase. For example, damage to the sensingunit 108 (such as a permanent dent) can cause the range of thedifferential voltage signal 312 to increase to 1.2V to 1.475V. Theelectronic circuit 122 can control the amplifier 314 to change theamplification level applied to the differential voltage signal 312 toaccount for this shift in the range of the differential voltage signal312 output by the bridge circuit 302. In this example, the electroniccircuit 122 can control the amplifier 314 to change the amplification toa 2× amplifier. This adjustment ensures that the signal received at theADC 316 is still greater than the unamplified signal, while keeping theoutput voltage range of the amplifier 314 within the acceptable voltagerange for the ADC 316. In this particular example, applying the 2×multiplier to the high end of the differential voltage signal 312 range(1.475V) leads to an output voltage of 2.95 from the amplifier 314,which is below the example maximum allowable voltage of 3V.

As another example, the range of values of the differential voltagesignal 312 that serves as the input to the amplifier 314 can change inresponse to other factors (as discussed above) other than or in additionto damage to the mobile computing device. For example, fatigue of thesensing unit 108 due to continued use can cause the range of thedifferential voltage signal 312 to increase over time. For example,after two years of use, the range of the differential voltage signal 312can increase to 700 mV to 975 mv. The electronic circuit 122 can controlthe amplifier 314 to change the amplification level applied to thedifferential voltage signal 312 to account for this shift in the rangeof the differential voltage signal 312 output by the bridge circuit 302.In this example, the electronic circuit 122 can control the amplifier314 to change the amplification to a 3× amplifier. This adjustmentensures that the signal received at the ADC 316 is still greater thanthe unamplified signal, while keeping the output voltage range of theamplifier 314 within the acceptable voltage range for the ADC 316. Inthis particular example, applying the 2× multiplier to the high end ofthe differential voltage signal 312 range (975 mV) leads to an outputvoltage of 2.925 from the amplifier 314, which is below the examplemaximum allowable voltage of 3V. In some implementations, the amplifier314 is restricted to amplification multipliers that are powers of 2. Insuch instances, in the above example in which the range of thedifferential voltage signal 312 increases to 700 mV to 975 mv, theelectronic circuit 122 can adjust the amplifier 314 to apply a 2×multiplier to the differential voltage signal 312 to avoid railing ofthe signal received at the ADC 316.

In some implementations, the electronic circuit 122 adjusts theamplification level of the amplifier 314 periodically. In someimplementations, the electronic circuit 122 adjusts the amplification ofthe amplifier 314 in response to a detected shift in a baseline outputvoltage of the bridge circuit 302 (or a detected shift in the baselineoutput voltage of the amplifier 314) that exceeds a predeterminedthreshold. In some implementations, the electronic circuit 122 adjuststhe amplification level of the amplifier 314 in response to detectedrailing of the output signal of the amplifier 314. For example, if theelectronic circuit 122 detects that the output of the ADC 316 is at ornear a maximum count value (e.g., 10,000 counts, or above 995 counts inan example in which the output range of the ADC 316 is 1 to 10,000counts) for a particular period of time, the electronic circuit 122 candetermine that railing has occurred (i.e., that the output voltage ofthe amplifier 314 is outside of the allowable input voltage range forthe ADC 316).

In some implementations, the electronic circuit 122 can perform aniterative process of continually stepping down the amplification levelof the amplifier 314 until a particular amplification level thatprevents railing is reached. In some implementations, the iterativeprocess includes maintaining the amplifier 314 at a particularamplification level for a predetermined period of time to determine ifrailing occurs within the period of time at the particular amplificationlevel.

In some implementations, the electronic circuit 122 can adjust theamplification level of the amplifier 314 in response to determining thatan output value of the amplifier 314 (or an output value of the ADC 316)has not exceeded a threshold value for a specified period of time. Forexample, if the output of the ADC 316 ranges from 1 to 10,000 counts,the electronic circuit 122 can increase the amplification level of theamplifier 314 in response to determining that the output value of theADC 316 has not exceeded 499 counts for a period of two days.

Continuing with FIG. 3, as discussed above, the bridge circuit 302produces a baseline differential voltage signal 312 when the sensingunit 108 is in an unpressed state. This baseline differential voltagesignal 312 is amplified by amplifier 314 and converted to a digitalquantized value by the ADC 316 such that the ADC 316 produces a baselineoutput value. The baseline differential voltage signal 312 (andconsequently the baseline output value of the ADC 316) can change overtime due to factors such as damage to the sensing unit 108, wear andtear, changes in temperature, changes in atmospheric pressure, ordegradation of components of the sensing unit 108 over time. Theelectronic circuit 122 can determine a baseline output value of the ADC316 over a period of time and use this baseline value to detectoccurrences of and the extent of user input. For example, the electroniccircuit 122 can sample for inputs at the sensing unit 108 (i.e.,pressure applied to the sensing unit 108) at a constant rate. Theelectronic circuit 122 can subtract the baseline output value of the ADC316 from the output value of the ADC 316 for each sample to determine adifferential between the output value for a particular sample and thebaseline output value. This determined differential value can then beused to determine if a user has applied pressure to the sensing unit 108and, in some cases, an extent or value of the pressure applied to thesensing unit 108.

The baseline output value of the ADC 316 can be determined using anumber of techniques. As a first example, the electronic circuit 122 canaverage the sampled output values of the ADC 316 over a particularperiod of time to identify the baseline value. However, applying asimple average can lead to an incorrect baseline output value of the ADC316 being identified as such an averaging technique would also includeoutput values when the sensing unit 108 is being pressed.

Another example technique that can be used to determine a baselineoutput value of the ADC 316 includes filtering out samples over a givenperiod of time that are indicative of a user pressing the sensing unit108 and averaging the output values for the remaining samples. Forexample, the electronic circuit 122 can apply a low pass filter (LPF) tooutput values sampled over a period of ten minutes. The LPF can filterout sudden changes in the output value of the ADC 316 that areindicative of a user pressing the sensing unit 108. For example, outputvalue increases that last for a period shorter than five seconds beforereturning to a substantially lower output value level can be filteredout. The remaining sampled output values are then averaged to determinethe baseline output value of the ADC 316. Another example technique thatcan be implemented by the electronic circuit 122 to determine a baselineoutput value of the ADC 316 includes using a high-pass filter with along period to track the baseline output value.

In some implementations, the process of determining/adjusting theidentified baseline output value of the ADC 316 is performedperiodically (e.g., every 10 minutes or every 2 hours). In someimplementations, process of determining/adjusting the identifiedbaseline output value of the ADC 316 is performed on a continual orrolling basis. For example, the electronic circuit 122 can continuallyidentify a baseline output value for a rolling 10-minute window as eachsample is measured. In other words, the baseline output value of the ADC316 identified by the electronic circuit 122 continually represents theprevious 10 minutes of recorded samples.

In some implementations, adjustment of the identified baseline outputvalue of the ADC 316 is triggered by one or more parameters. Forexample, the electronic circuit 122 can identify that an output value ofthe bridge circuit 302 has sharply increased and remained increased fora threshold period of time (e.g., 30 seconds, 1 minute, 2 minutes, 5minutes). Such a significant increase in the output value of the ADC 316that does not significantly decrease after a threshold amount of timecan indicate a permanent change in the baseline output value of the ADC316 such as, for example, due to the mobile device that includes thesensing unit 108 being dropped and causing damage to the sensing unit108 (e.g., a dent in a portion of the sensing unit 108). In response todetermining that the output value of the ADC 316 has increased andremained at the increased level for a particular period of time, theelectronic circuit 122 can adjust the identified baseline output valueof the ADC 316. For example, the adjusted identified baseline outputvalue of the ADC 316 can be an average of output values since the timeat which the sharp increase occurred after a LPF has been applied to thesamples recorded over that period of time. In some implementations, theelectronic circuit 122 adjusts the identified baseline output value ofthe ADC 316 in response to an increase in the output values of the ADC316 that exceeds a threshold value for a threshold period of time. Forexample, an increase in output values of the ADC 316 of 500 counts overthat persists for two minutes can trigger the electronic circuit 122 torecalculate the baseline output value of the ADC 316.

As described above, the electronic circuit 122 can compare sampledoutput values of the ADC 316 to the calculated baseline output value ofthe ADC 316 to determine that a user has pressed the sensing unit 108and, in some cases, the extent of the user input (e.g., whether thepress is a soft press, medium press, hard press, etc.). For example, theelectronic circuit 122 can subtract the calculated baseline output valueof the ADC 316 from the output value of the ADC 316 for a particularsample. The difference between the output value for the sample and thebaseline output value of the ADC 316 can then be categorized into avalue range to determine if the sensing unit 108 is being pressed andthe relative pressure being applied to the sensing unit 108. Forexample, the difference between the sensed output value and the baselineoutput value can be categorized into one of six discrete value ranges S0to S5, with values falling into the S0 category indicating that thesensing unit 108 is not being pressed and values falling into categoriesS1-S5 indicating increasing amounts of pressure being applied to thesensing unit 108.

In some implementations, the electronic circuit 122 can adjust theamplification level of the amplifier 314 in response to detecting achange in the calculated baseline output value of the ADC 316 thatexceeds a threshold value. For example, the electronic circuit 122 canadjust the amplification level of the amplifier 314 in response to thebaseline output value of the ADC 316 increasing from 500 counts to 2,000counts. As another example, an increase in the baseline output value ofthe ADC 316 of 1,000 counts can trigger the electronic circuit 122 toadjust the amplification level of the amplifier 314. As yet anotherexample, a decrease in the baseline output value of the ADC 316 of 1,000counts can trigger the electronic circuit 122 to adjust theamplification level of the amplifier 314.

In some implementations, the electronic circuit 122 can implement powermanagement processes to conserve electrical power in response to one ormore determined parameters. For example, the electronic circuit 122 canreduce a sampling rate for sampling output values of the ADC 316 inresponse to one or more determined parameters. The reduction in samplingrate conserves power for the computing device that includes the sensingunit 108.

In one example, the electronic circuit 122 can reduce the sampling ratefor output values of the ADC 316 in response to determining that thecomputing device is in a sleep mode. For example, the electronic circuit122 can use a sampling rate of 100 Hz when the computing device is in anactive mode and reduce the sampling rate to 10 Hz (or 1 Hz or 1/10 Hz)when the device is in sleep mode. As another example, the electroniccircuit 122 can reduce the sampling rate (e.g., to 10 Hz, 1 Hz, or 1/10Hz) in response to a determination that the computing device is pluggedinto a power supply and is positioned on a horizontal surface (asdetermined by one or more gyroscopes and accelerometers of the computingdevice). Such a determination can indicate that a user is unlikely tointeract with the sensing unit 108 and therefore that the sampling ratecan be reduced. As another example, the electronic circuit 122 canreduce the sampling rate in response to outputs from a proximitydetector. For example, if a proximity detector detects that thecomputing device is near an object, the electronic circuit 122 canreduce the sampling rate. As another example, the electronic circuit 122can reduce the sampling rate in response to a combination of theproximity sensor detecting that the computing device is near an objectand a touch screen (or other input) of the computing device notreceiving user input for a specified period of time. Such a combinationof parameters can indicate that the computing device is, for example, inthe users pocket and therefore that the user in unlikely to interactwith the sensing unit 108.

In some implementations, the electronic circuit 122 can increase thesampling rate in response to one or more determined parameters. Forexample, the electronic circuit 122 can increase the sampling rate from1 Hz to 100 Hz in response to the computing device transitioning from asleep mode to an active mode. As another example, the electronic circuit122 can increase the sampling rate in response to the proximity sensordetermining that the computing device is no longer near an object. Asanother example, the electronic circuit 122 can increase the samplingrate in response to one or more accelerometers of the computing devicedetermining that the computing device has been moved from a horizontalposition to a non-horizontal position, or has simply been moved in anydirection more than a threshold amount. As another example, theelectronic circuit 122 can increase the sampling rate in response to thecomputing device receiving a phone call or a notification such as an SMSmessage or a push notification from an application running on thecomputing device. The electronic circuit 122 can increase the samplingrate for a period of time in response to such an occurrence as the useris likely to want to respond to the received call or notification usingthe sensing unit 108.

In some implementations, the electronic circuit 122 can be configured toignore fluctuations in the output values of the ADC 316 in response toone or more parameters. For example, if the proximity sensor of thecomputing device indicates that the computing device is near an objectand the touch screen of the computing device is not receiving userinput, this can indicate that the computing device is in a user'spocket. In response to such a determination, the electronic circuit 122can ignore fluctuations in the output values of the ADC 316 that arebelow a particular threshold value as such fluctuations are likely dueto walking or running motion of the user.

FIG. 4 is a graph of changes to ambient temperature around a straingauge over time and corresponding changes to baseline output voltageoutput by a sensing unit, such as the sensing unit 108. In the exampleshown, the baseline output voltages are, for example, voltages output bya resistor bridge of the sensing unit prior to amplification of thevoltage signal or quantization of the voltage signal by ananalog-to-digital converter (ADC). As shown in FIG. 4, the baselinevoltage increases as ambient temperature increases and decreases asambient temperature increases. In the system described with respect toFIGS. 1-3, the changes in baseline output voltage lead to correspondingchanges in baseline output values of an ADC in electrical communicationwith the strain gauge.

As previously described, baseline output voltage is the differentialoutput voltage of sensing unit when the sensing unit is in an unpressedstate. Referring to both FIGS. 3 and 4, as the changes in baselineoutput voltage occur over time, the electronic circuit 122 cancontinually recalculate the baseline output value of the ADC 316 toadjust for the changes in baseline output voltage due to changes intemperature over time. As previously described, the electronic circuit122 can apply an LPF or HPF to eliminate samples indicative of a userpressing the sensing unit 108 and average the remaining samples over aperiod of time (e.g., the last 10 minutes) to calculate the baselineoutput value of the ADC 316. As previously described, variations inother factors over time in addition to temperature can cause thebaseline output voltage to change over time. For example, changes inatmospheric pressure, or degradation of a sensing unit 108 over time dueto continued use can cause the baseline output voltage to change overtime.

FIG. 5 illustrates a graph of changes to a sampling rate for a straingauge over time. As previously described, an electronic circuit of astrain gauge (such as the electronic circuit 122 of FIGS. 1 and 3) canadjust the sampling rate for sampling the output of an ADC in electricalcommunication with a strain gauge sensing unit (or, alternatively, thesampling rate for sampling the output of the sensing unit directly, oran amplifier in electrical communication with the sensing unit). Theelectronic circuit can adjust the sampling rate in response to one ormore detected parameters.

For example, in FIG. 5, the initial sampling rate for an electroniccircuit in communication with a strain gauge sensing unit is 100 Hz.This initial sampling rate can be a standard sampling rate when acomputing device that includes the strain gauge is in an active mode.The electronic circuit maintains the sampling rate of 100 Hz until timeT1. At time T1, the electronic circuit receives control signalsindicating that a proximity sensor of the computing device detects anearby object and that the touch screen of the computing device is notreceiving touch input. This information can be interested by theelectronic circuit to be indicative of the computing device being in aperson's pocket. In response to this determination, the electroniccircuit reduces the sampling rate to 10 Hz at time T1.

At time T2, the computing device returns to an active mode. For example,the user of the computing device can unlock the computing device oranswer an incoming phone call. In response to the computing devicereturning to the active mode, the electronic circuit raises the samplingrate to the active mode sampling rate of 100 Hz. At time T3, theelectronic circuit receives control signals indicating that thecomputing device is connected to a power source and is in a horizontalposition. This information can indicate that the computing device iscurrently charging and resting on a table or other flat surface. Inresponse to this received information, at time T3 the electronic circuitlowers the sampling rate to 1 Hz.

Embodiments of the subject matter and the functional operationsdescribed in this specification can be implemented in digital electroniccircuitry, in tangibly-embodied computer software or firmware, incomputer hardware, including the structures disclosed in thisspecification and their structural equivalents, or in combinations ofone or more of them. Embodiments of the subject matter described in thisspecification can be implemented as one or more computer programs, i.e.,one or more modules of computer program instructions encoded on atangible non-transitory program carrier for execution by, or to controlthe operation of, data processing apparatus.

Alternatively or in addition, the program instructions can be encoded onan artificially-generated propagated signal, e.g., a machine-generatedelectrical, optical, or electromagnetic signal that is generated toencode information for transmission to suitable receiver apparatus forexecution by a data processing apparatus. The computer storage mediumcan be a machine-readable storage device, a machine-readable storagesubstrate, a random or serial access memory device, or a combination ofone or more of them.

The processes and logic flows described in this specification can beperformed by one or more programmable computers executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit). Various implementations ofthe systems and techniques described here can be realized in digitalelectronic circuitry, integrated circuitry, specially designed ASICs,computer hardware, firmware, software, and/or combinations thereof.These various implementations can include implementation in one or morecomputer programs that are executable and/or interpretable on aprogrammable system including at least one programmable processor, whichmay be special or general purpose, coupled to receive data andinstructions from, and to transmit data and instructions to, a storagesystem, at least one input device, and at least one output device.

To provide for interaction with a user, the systems and techniquesdescribed here can be implemented on a computer having a display device,e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor,for displaying information to the user and a keyboard and a pointingdevice, e.g., a mouse or a trackball, by which the user can provideinput to the computer. Other kinds of devices can be used to provide forinteraction with a user as well; for example, feedback provided to theuser can be any form of sensory feedback, e.g., visual feedback,auditory feedback, or tactile feedback; and input from the user can bereceived in any form, including acoustic, speech, or tactile input.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the disclosed technology. For example, variousforms of the flows shown above may be used, with steps re-ordered,added, or removed. Also, although several applications of the straingauge sensing unit system and methods have been described, it should berecognized that numerous other applications are contemplated.Accordingly, other embodiments are within the scope of the followingclaims.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments. Certain features that are described in thisspecification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable subcombination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various system modulesand components in the embodiments described above should not beunderstood as requiring such separation in all embodiments, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

Particular embodiments of the subject matter have been described. Otherembodiments are within the scope of the following claims. For example,the actions recited in the claims can be performed in a different orderand still achieve desirable results. As one example, the processesdepicted in the accompanying figures do not necessarily require theparticular order shown, or sequential order, to achieve desirableresults. In some cases, multitasking and parallel processing may beadvantageous.

What is claimed is: 1.-20. (canceled)
 21. An apparatus for sensing userinput provided on an exterior surface of a device, comprising: a firststrain gauge configured to couple with a housing of an electronicdevice; an amplifier electrically coupled to the first strain gauge andconfigured to generate a plurality of analog signals by amplifying anelectrical property of the first strain gauge; an analog-to-digitalconverter electrically coupled to the amplifier and configured toreceive the plurality of analog signals from the amplifier and generatea plurality of digital signals that are representations of the pluralityof analog signals generated by the amplifier; and an electronic circuitelectrically coupled to the analog-to-digital converter and configuredto: (i) receive digital signals from the analog-to-digital converter,and (ii) implement a power management process to reduce powerconsumption by reducing a sampling rate at which the electronic circuitsamples digital signals output by the analog-to-digital converter from afirst sampling rate to a second sampling rate, the second sampling ratebeing lower than the first sampling rate.
 22. The apparatus of claim 21,wherein the electronic circuit is configured to reduce the sampling ratefrom the first sampling rate to the second sampling rate in response toone or more signals generated by one or more accelerometers of theelectronic device.
 23. The apparatus of claim 21, wherein the electroniccircuit is configured to reduce the sampling rate from the firstsampling rate to the second sampling rate in response to one or moresignals generated by one or more gyroscopes of the electronic device.24. The apparatus of claim 21, wherein the electronic circuit isconfigured to reduce the sampling rate from the first sampling rate tothe second sampling rate in response to a proximity detector of theelectronic device detecting an object within a threshold distance of theelectronic device.
 25. The apparatus of claim 21, wherein the electroniccircuit is configured to reduce the sampling rate from the firstsampling rate to the second sampling rate in response to (1) determiningthat the electronic device is within a threshold distance of an object,based on signals generated by a proximity detector of the electronicdevice; and (2) an input mechanism of the computing device not havingreceived user input for a specified period of time.
 26. The apparatus ofclaim 21, wherein the electronic circuit is configured to reduce thesampling rate from the first sampling rate to the second sampling ratein response to determining that electronic device has moved in aparticular direction more than a threshold amount
 27. The apparatus ofclaim 21, wherein the electronic circuit is configured to reduce thesampling rate from the first sampling rate to the second sampling ratein response to determining that the electronic device has entered asleep mode.
 28. The apparatus of claim 21, wherein the electroniccircuit is configured to reduce the sampling rate from the firstsampling rate to the second sampling rate in response to determiningthat the electronic device is in an inactive mode.
 29. The apparatus ofclaim 21, wherein the first sampling rate is approximately 100 Hz andthe second sampling rate is approximately 10 Hz.
 30. The apparatus ofclaim 21, wherein the electronic circuit is configured to reduce thesampling rate from the first sampling rate to the second sampling ratein response to determining that the electronic device is attached to adocking station.
 31. The apparatus of claim 21, wherein the electroniccircuit is configured to reduce the sampling rate from the firstsampling rate to the second sampling rate in response to determiningthat the electronic device is connected to a power source and ispositioned in a relatively horizontal position.
 32. A method ofcontrolling an electronic circuit of an electronic device, wherein theelectronic circuit is in operative communication with a first straingauge coupled to the housing of the electronic device, the methodcomprising: sampling, at a first sampling rate by the electroniccircuit, digital signals generated by an analog-to-digital converter inresponse to user input that interacts with the housing of the electronicdevice, the analog-to-digital converter configured to receive aplurality of analog signals generated by an amplifier in operativecommunication with the first strain gauge of the electronic device, theanalog-to-digital converter further configured to generate a pluralityof digital signals that are representations of the collections of analogsignals generated by the amplifier; identifying, by the electroniccircuit, a trigger event; and in response to identifying the triggerevent, sampling, at a second sampling rate by the electronic circuit,digital signals generated by the analog-to-digital converter, the secondsampling rate being different from the first sampling rate.
 33. Themethod of claim 32, wherein the trigger event is identified using one ormore signals generated by one or more accelerometers of the electronicdevice.
 34. The method of claim 32, wherein the trigger event isidentified using one or more signals generated by one or more gyroscopesof the electronic device.
 35. The method of claim 32, wherein thetrigger event comprises detection of an object within a thresholddistance of the electronic device by one or more proximity detectors ofthe electronic device.
 36. The method of claim 32, further comprising:determining that the one or more proximity detectors no longer detect anobject within the threshold distance of the electronic device; and inresponse to determining that the one or more proximity detectors nolonger detect an object within the threshold distance of the electronicdevice, sampling, at the first sampling rate by the electronic circuit,the digital signals generated by the analog-to-digital converter. 37.The method of claim 32, wherein the trigger event comprises theelectronic device entering a sleep mode.
 38. The method of claim 32,wherein the trigger event comprises the electronic device exiting asleep mode.
 39. The method of claim 32, wherein the trigger eventcomprises the electronic device transitioning from a relativelyhorizontal position to a relatively non-horizontal position.
 40. Themethod of claim 32, wherein the trigger event comprises the electronicdevice receiving an incoming communication.
 41. The method of claim 32,wherein identifying the trigger event is performed based on adetermination as to if the electronic device is connected to a powersource.
 42. An apparatus for sensing user input provided on an exteriorsurface of an electronic device, comprising: a first strain gaugeconfigured to couple with a housing of the electronic device; anamplifier electrically coupled to the first strain gauge and configuredto generate a plurality of analog signals by amplifying an electricalproperty of the first strain gauge; an analog-to-digital converterelectrically coupled to the amplifier and configured to receive theplurality of analog signals from the amplifier and generate a pluralityof digital signals that are representations of the plurality of analogsignals generated by the amplifier; and an electronic circuitelectrically coupled to the analog-to-digital converter and configuredto: (i) receive digital signals from the analog-to-digital converter,and (ii) increase a sampling rate at which the electronic circuitsamples digital signals output by the analog-to-digital converter from afirst sampling rate to a second sampling rate in response to a triggerevent, the second sampling rate being higher than the first samplingrate.
 43. The apparatus of claim 42, wherein the trigger event comprisesthe electronic device exiting a sleep mode.
 44. The apparatus of claim42, wherein the trigger event comprises the electronic device receivingan incoming communication.
 45. The apparatus of claim 42, wherein thetrigger event is identified using one or more signals generated by oneor more accelerometers of the electronic device.
 46. The apparatus ofclaim 42, wherein the trigger event is identified using one or moresignals generated by one or more gyroscopes of the electronic device.47. The apparatus of claim 42, wherein the trigger event is identifiedusing one or more signals generated by one or more proximity detectorsof the electronic device.